The present invention is an apparatus for dispensing various kinds of strings or threads or the like. In particular, the present invention relates to an apparatus for dispensing various different kinds of threads and strings et cetera which are coated with adhesives and which are applied to various web materials to laminate substrates together or to reinforce the web material.
Threads, strings, rovings and monofilaments which are coated with adhesives are known in the prior art and have been used to laminate web substrates together and/or reinforce web materials. The assignee of the present invention manufactures and distributes under the trade name LINEAR.RTM. adhesives and STRING KING.RTM. types of strings, threads and monofilaments coated with thermoplastic adhesive commonly referred to as "hot melt" adhesive. For example, a typical STRING KING product is a strand consisting of numerous continuous synthetic filaments uniformly coated with the thermoplastic hot melt adhesive. The hot melt adhesives are solids at normal ambient temperatures but become soft as they are heated and will flow at elevated temperatures. The apparatus of the present invention is specifically designed to feed STRING KING reinforcements onto web materials. In one such application that has found significant success the STRING KING reinforcements are utilized in the manufacture of corrugated board whereby the adhesive coated string is deposited between the liner board and flute in the continuous web manufacturing process.
The string adhesive products are typically supplied on cylinder rolls that may contain anywhere from 20,000 to 100,000 feet of string. The string is typically removed from the end of the individual rolls. Alignment of the string on the moving web to which it is applied is critical in many instances and therefore accurate placement is desired. Additionally, different industrial operations which use the string adhesives may operate at a variety of speeds. For example, it is not uncommon for corrugating operations to run at 200-300 feet per minute, but some are also known to run as slowly as 150 feet per minute or as fast as 600 feet per minute. Thus, the string adhesive dispensing device must be capable of feeding the string at whatever speed is demanded by the particular application. In many applications a number of such strings are used at the same time and the dispensing device must therefore be capable of handling a plurality of rolls of string.
The prior art dispensing system developed by the assignee of the present invention includes a dispensing rack on which may be mounted a plurality of rolls of string adhesive. A guide track is provided and mounted in a suitable location with respect to the corrugating machine or other moving web apparatus in order to guide the individual string adhesives onto the moving web. String adhesives are fed from the dispensing rack to the guide track through eye bolts, one each of which is provided on the rack for each roll of string adhesive. These eye bolts through which the string adhesive passes can be turned or oriented to adjust the tension on each individual string. It has been found that the proper control of the string tension is necessary to ensure a trouble-free operation. Too little tension often results in poor bonding and inaccurate string placement on the moving web. Excessive tension will obviously cause string breakage. It is desirable to operate with the minimum tension required to eliminate any slack in the string adhesive as it is guided onto the moving web.
Obviously, in the prior art apparatus, the tension on each individual string must be independently adjusted. Thus, it is almost physically impossible to maintain equal tension on the plurality of string adhesives as would be preferred. Additionally, in the prior art apparatus wherein the eye bolts are used to regulate the tension, it has been found that special care must be taken to ensure that all the eye bolts and guides remain smooth and have no rough surfaces that will increase drag.
Therefore, the dispensing apparatus of the present invention was developed to eliminate the tensioning problems associated with the prior art and to provide a dispensing apparatus wherein a single manual adjustment could be made to regulate the tension on all of the string adhesives fed from the dispensing apparatus and wherein equal tension could be established on each of the individual string adhesives. Thus, with the minimum of operator adjustment, tension on the individual strings can be regulated and maintained equally distributed over a plurality of such strings to ensure proper alignment and application of the string adhesives to the moving web in a particular application. In the apparatus of the present invention, the tension is also more accurately controlled as compared to the prior art wherein individual eye bolts had to be adjusted to provide the necessary drag on the string adhesive to develop the desired tension.